This invention relates to moving storage apparatus wherein a transducer head is in contact with the storage medium surface when the storage medium is at rest and is separated from the storage medium by a fluid film when the medium is moving at operational speed and, more particularly, to a reduced media speed low power mode for such a device.
Most disk drive data storage devices experience prolonged periods of data read/write inactivity. This is particularly true for devices that run continuously overnight or during holidays. Maintaining the standby operation is a waste of energy that is a critical consideration where the system is powered from a limited power source such as the batteries of a portable device or where heat dissipation is a problem. As microcomputers become ubiquitous in the work place and tend to be continuously operational, there have appeared requirements that the power consumption of such systems meet reduced standards of power consumption. Completely powering down the device requires a relatively long wait for the drive to become ready to read or write data and frequent power on and off cycles result in increased wear and possible high stiction events that reduce the useful life of the disk storage equipment. Thus, during idle periods it is desirable to reduce power consumption while maintaining a near operational status of the device.
During idle periods, the principal power consumption is by the spindle motor, which normally maintains the full rotational velocity of the disk media despite the absence of read or write operations. The voice coil actuator motor is not required to provide access or track-follow functions and the solid state control circuitry has minimal energy requirements. With a reduction of spindle motor speed, the voice coil motor will experience fewer servo signals and make correspondingly fewer corrections such that the reduced power consumed by the spindle motor will result in a reduction of the power used by the actuator voice coil motor. In environments where the actuator is maintained at an inner or outer crash stop by a permanent magnet field, the supply of power to the actuator voice coil motor can be effectively terminated during reduced speed operation.
In the past it has been suggested that the disk drive spindle motor rotational velocity be reduced during idle periods. Reducing the spindle and media rotational velocity saves power, but also risks causing a transducer head to drag on the disk surface if the media velocity is not set correctly. Ideally, the media velocity would be reduced to the minimum possible value for the particular drive to take full advantage of the increased power savings to be obtained by lower speeds. Current approaches for motor speed reduction have no way to insure that a head or heads are not sliding on the disk, which would lead to premature failure. The only manner in which present techniques are able to reduce spindle velocity safely is by decreasing the rotational velocity by the magnitude dictated by the worst case head. This constraint means that current methods do not allow the velocity to be reduced by the maximum allowable amount for each disk drive.